The present invention generally relates to air purification systems, and more particularly, to an air purification system and method using a photocatalyst and ultraviolet light emitting diodes (UV-LEDS) operated with a duty cycle.
The use of recirculated air may be common within inhabited enclosures. In some cases, airflow may be necessarily recirculated to provide breathable air where air external to the enclosure may not be viable. In other cases, it may be more economical to use recirculated air which has already been adjusted to the correct temperature and humidity. For example, pressurized cabins in aircraft may commonly recirculate a portion of the air rather than try to circulate only external air into the cabin. One result of using recirculated air is that organic contaminants, including volatile organic compounds (VOCs), may increase in concentration to undesirable levels, and may be passed to the inhabitants of the cabin.
One approach to removing contaminants from airflow is to use a photocatalytic air cleaner on airflow. It may be known to use, for example, an array of UV-LEDs to irradiate a photocatalyst in contact with the airflow. Although this may result in removing contaminants from the airflow through an oxidation process, the radiation from the UV-LEDs may also heat the airflow. Additional power may then be expended downstream of the photocatalyst to cool the airflow. In some applications, for example, an aircraft or other vehicle, any additional power usage may result in reduced fuel efficiency. In addition, weight may be added to the system if heavier or additional components, such as a larger fan, are necessary to accomplish the cooling. This may result in reduced cargo or passenger capacity.
Reducing the radiation of the UV-LEDs to the minimum level necessary to meet a desired contaminant reduction target may result in lower power consumption and lower airflow heat absorption. However, in some cases, when radiation levels are reduced, although the reduction target for some contaminants may be met, the concentration level of by-products produced in the oxidation process may exceed a desired level. For example, ethanol levels in airflow may be reduced through oxidation with a photocatalytic device. At lower radiation levels, however, the oxidation process may increase the concentration of acetaldehyde in the airflow to an unacceptable level. To additionally meet a desired target for by-product concentration, a higher power level may be needed than the power level necessary to only reduce the contaminant levels.
As can be seen, there may be an ongoing need for a system and/or method to reduce the concentration of contaminants and by-products in recirculated airflow at lower power levels.